19-4778; Rev 0a; 8/98
MAX668 Evaluation Kit
General Description
The MAX668 evaluation kit (EV kit) combines a con-
stant-frequency, pulse-width-modulation (PWM) step-
up controller with an external N-channel MOSFET and
Schottky diode to provide a regulated output voltage.
The EV kit accepts a +3V to V
OUT
input and converts it
to a +12V output for currents up to 1A, with greater than
90% conversion efficiency. The EV kit operates at
500kHz, allowing the use of small external components.
The MAX668 EV kit is a fully assembled and tested sur-
face-mount circuit board. This EV kit can also be con-
figured for the application circuits listed in the
EV Kit
Application Circuit Capabilities
table. For input voltages
below 3V and down to 1.8V, replace the MAX668 with a
MAX669. The MAX669 must always operate in boot-
strapped mode (JU2 shunt across pins 1 and 2).
o
+12V or Adjustable Output Voltage
o
Output Current Up to 1A
o
N-Channel External MOSFET
o
4µA IC Shutdown Current
o
500kHz Switching Frequency
o
Surface-Mount Components
o
Fully Assembled and Tested
Features
o
+3V to V
OUT
Input Range (as shipped)
Evaluates: MAX668/MAX669
Component List
DESIGNATION QTY
C1
1
DESCRIPTION
68µF, 20V, low-ESR tantalum cap
Sprague 593D686X0020E2W or
AVX TPSE686M020R0150
120µF, 20V, low-ESR tantalum cap
Sprague 594D127X0020R2T
0.1µF ceramic capacitor
0.22µF ceramic capacitor
1µF ceramic capacitors
220pF ceramic capacitor
Not installed
3A Schottky diode
Hitachi HRF302A or
Motorola MBRS340T3
4.7µH power inductor
Sumida CDRH104-4R7 (shielded),
Coiltronics UP2B-4R7, or
Coilcraft DO3316P-472
N-channel MOSFET
Fairchild FDS6680 or
International Rectifier IRF7801
0.020Ω, 1%, 1/2W resistor
Dale WSL-2010-R020F or
IRC LR2010-01-R020F
218kΩ, 1% resistor
24.9kΩ, 1% resistor
100kΩ, 1% resistor
MAX668EUB
3-pin headers
2-pin header
Shunts (JU1, JU2)
MAX668/MAX669 PC board
MAX668/MAX669 data sheet
1
Ordering Information
C5
PART
MAX668EVKIT
TEMP. RANGE
0°C to +70°C
IC PACKAGE
10 µMAX
C2
C3
C4, C8
C7
C6
1
1
2
1
0
1
1
Note:
To evaluate the MAX669, request a MAX669EUB free
sample with the MAX668EVKIT.
EV Kit Application Circuit
Capabilities
V
IN(MIN)
(V)
1.8
1.8
2.5
3
3
3
12
V
OUT
(V)
12
24
12
5
12
36
24
I
OUT
(A)
0.4
0.1
0.65
3
1
0.02
0.5
D1
L1
1
N1
1
R1
R2
R3
R4
U1
JU1, JU2
JU3
None
None
None
1
1
1
1
1
2
1
2
1
1
Note:
Design information for these applications is included.
The shaded row shows EV kit configuration as shipped.
________________________________________________________________
Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
MAX668 Evaluation Kit
Evaluates: MAX668/MAX669
Component Suppliers
SUPPLIER
AVX
CoilCraft
Coiltronics
Dale-Vishay
Fairchild
Hitachi
International
Rectifier
IRC
Motorola
Siliconix
Sprague
Sumida
Vishay/Vitramon
PHONE
803-946-0690
708-639-6400
561-241-7876
402-564-3131
408-721-2181
888-777-0384
310-322-3331
512-992-7900
602-303-5454
408-988-8000
603-224-1961
708-956-0666
203-268-6261
FAX
803-626-3123
708-639-1469
561-241-9339
402-563-6418
408-721-1635
650-244-7947
310-322-3332
512-992-3377
602-994-6430
408-970-3950
603-224-1430
708-956-0702
203-452-5670
Note:
Please indicate that you are using the MAX668 when con-
tacting these component suppliers.
If the minimum input voltage is below +3.0V, use the
MAX669 with V
CC
bootstrapped from V
OUT
(Table 1). In
bootstrapped mode, if V
OUT
is always less than +5.5V,
then LDO may be shorted to V
CC
to eliminate the
dropout voltage of the LDO regulator. This increases the
gate drive to the MOSFET, which lowers the MOSFET
on-resistance but increases the MAX668 supply current
due to gate-charge loss.
If V
IN
is greater than +3.0V, the MAX668’s V
CC
can be
powered from V
IN
. This will decrease quiescent power
dissipation, especially when V
OUT
is large. If V
IN
is
always less than +5.5V, LDO may be shorted to V
CC
to
eliminate the dropout voltage of the LDO regulator. If
V
IN
is in the range of +3V to +4.5V, then the user may
still want to bootstrap from V
OUT
to increase gate drive
to the MOSFET at the expense of power dissipation. If
V
IN
is always greater than +4.5V, the V
CC
input should
always be tied to V
IN
, since bootstrapping from V
OUT
will not increase the gate drive from LDO, but quiescent
power dissipation will rise. Jumpers JU2 and JU3 con-
trol the V
CC
and LDO inputs (see
MAX668/MAX669
data sheet).
Jumper Selection
_________________________Quick Start
The MAX668 EV kit is fully assembled and tested. Follow
these steps to verify board operation.
Do not turn on
the power supply until all connections are completed.
1) Place the shunt on JU1 across pins 1 and 2. Verify
that the shunt is across JU2 pins 2 and 3 (V
CC
is
tied to V
IN
) and JU3 is open (LDO is open).
2) Connect a +5V supply to the V
IN
pad. Connect
ground to the GND pad.
3) Connect a voltmeter to the V
OUT
pad.
4) Turn on the power supply and verify that the output
voltage is 12V.
The 3-pin header JU1 selects shutdown mode. Table 1
lists the selectable jumper options. The 3-pin header
JU2 selects bootstrapped mode. Table 2 lists the
selectable jumper options. For V
CC
less than 5.5V, use
the 2-pin header JU3 to short LDO to V
CC
. This elimi-
nates the internal linear regulator (LDO) dropout volt-
age. For the MAX668, this allows operation with input
voltages down to 2.7V. Table 3 lists the selectable
jumper options.
Other Output Voltages
The MAX668 EV kit can also be used to evaluate other
output voltages. Refer to the
Output Voltage Selection
section in the MAX668 data sheet for instructions on
selecting the feedback resistors R2 and R3.
For output
voltages greater than 15V, replace C5 (20V) with a
capacitor that has a higher voltage rating.
In addition to the standard EV kit configuration of 3V
IN
to 12V
OUT
at 1A, the
EV Kit Application Circuit
Capabilities
table listed several common Input/Output
combinations. Table 4 lists the components recom-
mended for these alternative circuits.
_______________Detailed Description
The MAX668 EV kit provides a regulated +12V output
voltage from an input source as low as +3V. It drives
loads up to 1A with greater than 90% conversion effi-
ciency. This EV kit is shipped configured in the non-
bootstrapped mode (V
CC
is tied to V
IN
). However, there
are several methods of connecting V
CC
and LDO
depending on the specific design including input and
output voltage range, quiescent power dissipation,
MOSFET selection, and load.
2
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